PREDICTION OF EXCRETION OF MANURE AND NITROGEN BY HOLSTEIN DAIRY-CATTLE

A compilation of N balance data (n = 1801) was partitioned into four g roups to define the mean excretion of manure and N and to develop empi rical equations to estimate these excretions from Holstein herds. Mean excretion of manure for cows that averaged 29 kg/d of milk production was 3 kg/d per 1000 kg of body weight (BW) more than the value for da iry cows reported by the American Society of Agricultural Engineers; N excretion was 0.09 kg/d per 1000 kg of BW higher than the value repor ted by the American Society of Agricultural Engineers. Mean excretion of manure and N for cows that averaged 14 kg/d of milk production and that for nonlactating cows were substantially lower than the values re ported by the American Society of Agricultural Engineers. Growing and replacement cattle excreted 10 kg/d per 1000 kg of BW more manure and 0.11 kg/d per 1000 kg of BW more N than was reported by the American S ociety for Agricultural Engineers for beef cattle. Estimation of manur e and N excretion was more accurate than mean values when using regres sion equations that included variables for milk production, concentrat ion of crude protein and neutral detergent fiber in the diet, BW, days in milk, and days of pregnancy. Equations that contained intake varia bles did not significantly affect predictions of manure and N excretio n, and the use of such equations is discouraged unless dry matter inta ke is measured and not estimated. Accurate estimates of excreta output could improve the planning of storage and handling systems for manure and the calculation of nutrient balances on dairy farms.